Ogbonnaya Igwe - Academia.edu (original) (raw)
Papers by Ogbonnaya Igwe
Journal of Petroleum Exploration and Production Technology
Carbon capture and sequestration technology has been a ground-breaking tool in tackling carbon di... more Carbon capture and sequestration technology has been a ground-breaking tool in tackling carbon dioxide (CO2) emissions worldwide but has limitedly been researched and practised in Africa at present. Considering the vast growth and developmental level in the continent, there is a need to consider this option of mitigating global climate change. In this study, a systematic and process-based incorporation of seismic and well logs datasets was used to characterize the structural and stratigraphic framework of sandstone reservoirs within the field in order to determine their capacities for effective CO2 sequestration. Petrophysical analysis, fault modelling as well as geostatistical techniques were used to build facies and property models which enabled a qualitative assessment of the sealing potential of faults associated with the reservoirs based on prediction of key properties such as shale gouge ratio, lithological juxtaposition, fault permeability and fault transmissibility across th...
Arabian Journal of Geosciences, 2014
Field and Shuttle Radar Topographic Mission data were used to create Digital Elevation Model and ... more Field and Shuttle Radar Topographic Mission data were used to create Digital Elevation Model and geologic maps to study the roles of geology, discontinuities, elevation, steep slopes, deep valleys, and drainage patterns on the frequent occurrence of long-travel landslides along the Nigeria-Cameroon border. The undrained shear behaviors of sandy specimens from two localities with different mode and magnitude of landslides were analyzed at different stress levels and related directly to their compressibility and permeability characteristics. The weathered granitic-sandy specimens from Kwande debris avalanche showed significant change in bulk permeability and sample height, and exhibited the greatest evidence of grain crushing. This behavior correlates well with their shear response which manifested in considerable increase in excess pore pressure and drastic reduction of shear resistance. Due to grain crushing, finer grains that lowered permeability were formed at the shear zone. It is likely that the decrease in permeability facilitated the generation of high excess pore pressures leading to significant reduction of shear resistance to low values at steady state. Contrastingly, the reduction in sample height and permeability of Iva valley sands was not as significant, which also correlates with the generation of low excess pore pressure and higher steady state strengths; conditions that may be responsible for the predominance of short-travel slides in the area. The behavior of silica sands, however, which suffered higher grain crushing and reduction in sample height and permeability, appeared closer to that of the samples from the avalanche site.
Environmental Earth Sciences, 2013
This paper analyses the dominant mechanisms of slope failures and identifies potential obstacles ... more This paper analyses the dominant mechanisms of slope failures and identifies potential obstacles to landslidehazard reduction at the Iva Valley area, Enugu, Nigeria. The landscape is replete with landslide scars and gullies of varied sizes and the slope deposits comprise unconsolidated, friable sands inter-bedded with thin units of montmorillonitic claystone. Forty-three landslide events were identified in the study area with most being shallow, short run-out movements with slip-surface depth\2 m. The study found the landslides mainly occur in the beginning of rainy season characterized by short duration, high intensity rainfall. An integrated approach comprising field mapping, laboratory tests and numerical analyses reveals that the barren nature of the slopes prior to the outset of rainy season, high rainfall intensity, erosion, overgrazing, soil characteristics and the site's unique lithologic sequence are the main causes of instability. Shearing tests under several conditions showed that the soils strongly strain-soften until low steady-state strength is achieved. A computer code, based on this strength reduction technique, used input parameters obtained from the field and laboratory studies to simulate a landslide with similar structure, travel distance and distribution area. It is noted that urbanization has gradually increased the vulnerability of the society's poor to landslide hazards as they now erect unplanned residence (tents and blocks) on the slopes. This work is part of a regional study aimed at finding ways of protecting the vulnerable by generating data that could be used to build future landslide susceptibility map.
Landslides, 2013
The ICL/IPL Project achieved results in capacity building, investigation of landslides in West Af... more The ICL/IPL Project achieved results in capacity building, investigation of landslides in West Africa and also evaluated some other slope movements in the region. These include the catastrophic rock–debris avalanche at the Cameroon–Nigeria border and the Iva Valley landslides in Enugu. During the avalanche, an estimated 100 M m3 of rock and debris was moved more than 2 km from the source of the slide at 600 m above sea level to the toe in the valley in a few minutes. The materials range from mud and soil debris to blocks of rocks up to 20 m in diameter. The grain size of moved material tended to increase upslope and closer to the head scarp though it tended to decrease again close to and at the source area. Nature and composition of the basement bedrock with foliation planes dipping in the direction of slope, dominant joint sets oriented perpendicularly to the foliation, the nature of weathered material and high relief were strong factors in the avalanche. Field studies identified 43 landslides at the Iva Valley area of Enugu state, which were shallow, short run-out movements with slip-surface depth less than 2 m. The shallow slides and the avalanche are triggered by water infiltration in slopes with high topographic gradient. The soil saturation leads to a reduction of the shear strength of the soil because of a rise in pore water pressure. These landslides are known to occur during or after intense rainfalls at the beginning or at the tail end of rainy season.
Arabian Journal of Geosciences, 2014
The Iva Valley area has one of the highest densities of landslides in Nigeria, and impacts the re... more The Iva Valley area has one of the highest densities of landslides in Nigeria, and impacts the residents, local economy, and the environment. Slopes in the area sit on unconsolidated, cross-bedded, friable sandstone units with interbeds of claystone. Past research efforts had proposed theories explaining the mechanism of failure based on the limited-liquefaction behavior of the slope materials. But as landslide prevention works on the slopes began to fail, it became apparent that those theories were inadequate solutions to the devastating effect of mass wasting processes. This paper presents the results of landslide susceptibility assessment based on the new evidence of complete-liquefaction behavior observed in the samples when back-pressure is employed to accomplish full saturation. Loose, saturated specimens failed after attaining maximum strength at shear displacements less than 1 mm. The failure was marked by rapid reduction in shear strength and accompanied by a steady increase in pore water pressure until the ratio of pore pressure and normal stress approached unity indicating complete liquefaction. This behavior simulated the response of the slope soils to varying stress and drainage conditions in the field, and seems an adequate mechanism for the incessant failure of slopes and prevention works. Because the geology of a vast area of the SouthEast Nigeria is similar, the results obtained at the study area are also applicable in other areas within the region for sustainable preventive and mitigating measures.
Geosciences Journal, 2013
ABSTRACT The dominant factors initiating the transformation of landslides into catastrophic debri... more ABSTRACT The dominant factors initiating the transformation of landslides into catastrophic debris flow are examined. The research found that a threshold pore pressure determined from theoretical and experimental analysis was enough to initiate liquefaction type of failure in sandy materials. Loading tests to failure on sourcearea sandy soils from a catastrophic landslide location show that under definite conditions of loading, a threshold state, characterized by the equality and constancy of pore pressure and shear resistance develops in the sands at a threshold density. Sands at this density clearly define the boundary between contractive and dilative specimens under same effective normal stress. Confirmatory experiments were then conducted using silica sand. Analyses showed that samples in which the threshold pore pressure was exceeded readily liquefied while those in which the pore pressure was below the limit dilated. The concept of threshold pore pressure fills the gap created by classical theories of soils liquefaction that have identified densities at which phase transformation and steady state lines can be defined. The new concept shows there is a density at which both lines merge and it is proposed that sands transiting from dense to loose and vice versa will first pass through the threshold state. While the stability of a slope founded on sandy soils may be breached when the pore pressure exceeds a certain limit, it is possible to make estimates of the limit. Where such estimates are accompanied with adequate field measurements, the effectiveness of landslide prevention projects may be enhanced.
Environmental Science and Pollution Research
Modeling Earth Systems and Environment
Arabian Journal of Geosciences
Indian Geotechnical Journal
Geosystems and Geoenvironment
Advancing Culture of Living with Landslides, 2017
Complex rock-debris avalanches, debris flow, soils slip and earth slumps in Nigeria lead to the d... more Complex rock-debris avalanches, debris flow, soils slip and earth slumps in Nigeria lead to the destruction of lives and resources worth several millions of dollars annually. While long travel landslides, which are almost always catastrophic, mostly occur on igneous and metamorphic terrains at the boundary of Nigeria and Cameroon, the south east sedimentary terrains are subject to deep and wide gullies resulting from aggressive erosion and slumping movements. Slope failures in the two regions are therefore distinctively different with research revealing that the differences are in geology, structural geometry, style of deformation, slope gradient and the volumes involved. At the Nigeria-Cameroon border, complex, rock-debris avalanches are found on steep dipping slopes, where slope parallel, basal sliding planes along foliation and lineation surfaces control failure and mobility of materials downslope.
Bulletin of Engineering Geology and the Environment, 2022
Soil erosion is a life-threatening hazard ravaging and displacing many communities in Anambra Sta... more Soil erosion is a life-threatening hazard ravaging and displacing many communities in Anambra State, Nigeria. Most erosion studies in this region have been based on geological and geotechnical analyses of soils from gullies. In this paper, the soil erosion risk of Anambra State was evaluated using the Revised Universal Soil Loss Equation (RUSLE) and geoinformatics, to estimate the rate of soil loss and identify vulnerable erosion zones. The RUSLE model was based on five erosion factors (rainfall erosivity (R), soil erodibility (K), topography (LS), vegetation cover (C), and anti-erosion practices (P)). The R-factor ranged from 460.51 to 582.08 MJ/mm/ha−1 h−1 year−1 whereas the K-factor ranged from 0.100 to 0.310 t/h/MJ−1/mm−1. Low–moderate LS-factor values dominated the northern and western portions of the State. However, moderate–high LS-factor scores dominated the eastern and southern portions. The C-factor varied from 0 (in areas covered by water bodies) to 1 (for barren lands). The P-factor ranged from 0.5–1. These five factors were integrated to generate soil loss rates across Anambra. The average annual soil loss ranged from 0 to over 6 t/ha−1 year−1. The soil loss results showed that about 5% (242.2 km2), 25% (1211 km2), 30% (1453.2 km2), and 40% (1937.6 km2) of the total area have very low, low, medium, and high erosion risks, respectively. The northern and western portions of the State were characterized by very low, low, and moderate soil loss. However, the eastern and southern portions were characterized by high soil loss rate. It was indicated that LS, K, and R are the most important soil loss factors in Anambra.
Environmental Earth Sciences, 2021
Over many decades, land degradation, due to gully erosion and landsliding, has remained a serious... more Over many decades, land degradation, due to gully erosion and landsliding, has remained a serious threat to land-use management and economic sustainability in southeastern Nigeria. Several causative factors have been listed to be responsible for the continuous land degradation. In this study, multiple geostatistical and new indexical models were integrated to assess the role of soil engineering properties in the erosion of ten major gullies in southern Anambra State, southeast Nigeria. Gully soil samples were analyzed for properties such as particle size distribution, water content, Atterberg limits, compactness, bulk density, specific gravity, shear strength, porosity and permeability coefficients. The geotechnical analyses revealed that the gully materials are weak and have poor erosion-resistant features. The results revealed that the soils’ engineering properties influence their erodibility. Interparameter relationships observed from correlation, factor, and cluster analyses showed that the engineering parameters jointly impact the erosion processes. Novel indexical methods, sand-gravel ratio (SGR) and sand–fines ratio (SFR), alongside erodibility factor confirmed that the soils are erodible. A novel entropized soil loss rate (AE) model estimated high cumulative annual soil loss rate for the area at 0.9705. Overall, it was revealed that SW, SC, and SP soils are far more susceptible to gully erosion than CL and GP soils in the area. Artificial neural network models were developed and used to accurately (with low model errors and R2 range of 0.956–0.997) predict the SGR, SFR and AE. The findings of this research would be helpful in advancing soil erosion investigations and in planning for effective mitigation measures, with respect to engineering properties.
Environmental Forensics, 2021
The effect of waste dumps on groundwater quality on perched aquifers in Nsukka and environs was i... more The effect of waste dumps on groundwater quality on perched aquifers in Nsukka and environs was investigated by applying multivariate statistical analyses using Statgraphics Centurion XVII, ArcGIS ...
Goldschmidt Abstracts, 2020
Gully erosion is a major environmental problem in Gombe town, large area of land is becoming unsu... more Gully erosion is a major environmental problem in Gombe town, large area of land is becoming unsuitable for human settlement, hence the need for gully erosion susceptibility map of the study area.To generate gully inventory map, detailed field exercise was carried out, during this investigation one hundred gullies were identified and studied extensively within the study area of about 550 km2. In addition to the mapped gullies, Google EarthPro with high resolution imagery was used to locate the spatial extents of fifty (50) more gullies. Ten gully erosion predisposing factors were carefully selected considering the information obtained from literature, and multiple field survey of the study area, the factors include: elevation, slope angle, curvature, aspect, topographic wetness index (TWI),soil texture, geology, drainage buffer, road buffer and landuse.In this study, a GIS-based Frequency Ratio (FR) and Analytical Hierarchy process (AHP) models were employed to predict areas prone t...
Modeling Earth Systems and Environment, 2020
Quality of the soil and its effect on groundwater pollution were evaluated using combined techniq... more Quality of the soil and its effect on groundwater pollution were evaluated using combined techniques of geotechnical, physicochemical, pollution indices and statistical models. Geotechnical result showed that particle sizes of soil in the study area are well graded. The physicochemical parameters (Zn, Cu, Cd, Pb, Mn, Fe, Cr and Ni) are higher in the control than in study area except for the soil pH. These parameters are within the standard set by Department of Petroleum Resources in Nigeria (DPR) for metal concentration in the soil. The ecological risk factor reviewed that toxicity of the element is potentially very low and PIavg and PIVector of the soil samples showed they are not contaminated. In contrast, the concentrations of these parameters including total dissolved solid TDS, biochemical oxygen demand BOD, turbidity were higher in groundwater samples from the study area than in control except for the groundwater pH (55.929) which was lower than in control (5.956). One of the 15 samples is out of the standard for Ni, Cu, Cd, Pb and Mn and two (2) for turbidity, Cr and Fe. Principal component analysis shows five factors accounting for 94.923% of the total variance. At 0.05 levels, very strong significant correlation and at 0.01 levels moderate to weak correlation exist between the elements. The result showed that groundwater from well-graded soil is of good quality irrespective of the industrial activities, whereas those from poorly graded soil are of poor quality.
Modeling Earth Systems and Environment, 2020
In Udi province, gully erosion has caused several environmental damages such as loss of agricultu... more In Udi province, gully erosion has caused several environmental damages such as loss of agricultural lands and natural vegetation, loss of residential apartments, destruction of engineering structures, and disruption of wildlife ecosystem. In this paper, an attempt was made to assess the erodibility characteristics and slope stability of geological units prone to erosion in this area using integrated approach. Geotechnical analysis of soil samples revealed that they are susceptible to erosional processes. The soil samples were classified as poorly graded sands and silty sands based on Unified Soil Classification System. Grain size distribution analysis showed that the soils were almost devoid of clays, which could serve as binding materials. Atterberg limit test revealed that they were nonplastic. Compaction test indicated that the soils were loose and collapsible, with dry density ranging from 1.65 to 1.96 g/cm 3. On the basis of permeability coefficients (which ranged from 6.81 × 10-5 to 1.28 × 10-4 m/s), the soils are moderately to highly permeable, indicating high infiltration capacity. Shear strength analysis revealed that the soils have low cohesive capacity (ranging from 0 to 5 kPa) and relatively low angle of shearing resistance (ranging from 22° to 30°). Multivariate statistical analyses aided the establishment of the interrelationships between the analyzed geotechnical parameters. The obtained factor of safety of the gully slopes (in both saturated and unsaturated conditions) ranged from 0.81 to 0.90 and 1.02 to 1.41, respectively. This indicates that the gully slopes are typically unstable in saturated conditions and critically stable in unsaturated conditions.
Journal of Petroleum Exploration and Production Technology
Carbon capture and sequestration technology has been a ground-breaking tool in tackling carbon di... more Carbon capture and sequestration technology has been a ground-breaking tool in tackling carbon dioxide (CO2) emissions worldwide but has limitedly been researched and practised in Africa at present. Considering the vast growth and developmental level in the continent, there is a need to consider this option of mitigating global climate change. In this study, a systematic and process-based incorporation of seismic and well logs datasets was used to characterize the structural and stratigraphic framework of sandstone reservoirs within the field in order to determine their capacities for effective CO2 sequestration. Petrophysical analysis, fault modelling as well as geostatistical techniques were used to build facies and property models which enabled a qualitative assessment of the sealing potential of faults associated with the reservoirs based on prediction of key properties such as shale gouge ratio, lithological juxtaposition, fault permeability and fault transmissibility across th...
Arabian Journal of Geosciences, 2014
Field and Shuttle Radar Topographic Mission data were used to create Digital Elevation Model and ... more Field and Shuttle Radar Topographic Mission data were used to create Digital Elevation Model and geologic maps to study the roles of geology, discontinuities, elevation, steep slopes, deep valleys, and drainage patterns on the frequent occurrence of long-travel landslides along the Nigeria-Cameroon border. The undrained shear behaviors of sandy specimens from two localities with different mode and magnitude of landslides were analyzed at different stress levels and related directly to their compressibility and permeability characteristics. The weathered granitic-sandy specimens from Kwande debris avalanche showed significant change in bulk permeability and sample height, and exhibited the greatest evidence of grain crushing. This behavior correlates well with their shear response which manifested in considerable increase in excess pore pressure and drastic reduction of shear resistance. Due to grain crushing, finer grains that lowered permeability were formed at the shear zone. It is likely that the decrease in permeability facilitated the generation of high excess pore pressures leading to significant reduction of shear resistance to low values at steady state. Contrastingly, the reduction in sample height and permeability of Iva valley sands was not as significant, which also correlates with the generation of low excess pore pressure and higher steady state strengths; conditions that may be responsible for the predominance of short-travel slides in the area. The behavior of silica sands, however, which suffered higher grain crushing and reduction in sample height and permeability, appeared closer to that of the samples from the avalanche site.
Environmental Earth Sciences, 2013
This paper analyses the dominant mechanisms of slope failures and identifies potential obstacles ... more This paper analyses the dominant mechanisms of slope failures and identifies potential obstacles to landslidehazard reduction at the Iva Valley area, Enugu, Nigeria. The landscape is replete with landslide scars and gullies of varied sizes and the slope deposits comprise unconsolidated, friable sands inter-bedded with thin units of montmorillonitic claystone. Forty-three landslide events were identified in the study area with most being shallow, short run-out movements with slip-surface depth\2 m. The study found the landslides mainly occur in the beginning of rainy season characterized by short duration, high intensity rainfall. An integrated approach comprising field mapping, laboratory tests and numerical analyses reveals that the barren nature of the slopes prior to the outset of rainy season, high rainfall intensity, erosion, overgrazing, soil characteristics and the site's unique lithologic sequence are the main causes of instability. Shearing tests under several conditions showed that the soils strongly strain-soften until low steady-state strength is achieved. A computer code, based on this strength reduction technique, used input parameters obtained from the field and laboratory studies to simulate a landslide with similar structure, travel distance and distribution area. It is noted that urbanization has gradually increased the vulnerability of the society's poor to landslide hazards as they now erect unplanned residence (tents and blocks) on the slopes. This work is part of a regional study aimed at finding ways of protecting the vulnerable by generating data that could be used to build future landslide susceptibility map.
Landslides, 2013
The ICL/IPL Project achieved results in capacity building, investigation of landslides in West Af... more The ICL/IPL Project achieved results in capacity building, investigation of landslides in West Africa and also evaluated some other slope movements in the region. These include the catastrophic rock–debris avalanche at the Cameroon–Nigeria border and the Iva Valley landslides in Enugu. During the avalanche, an estimated 100 M m3 of rock and debris was moved more than 2 km from the source of the slide at 600 m above sea level to the toe in the valley in a few minutes. The materials range from mud and soil debris to blocks of rocks up to 20 m in diameter. The grain size of moved material tended to increase upslope and closer to the head scarp though it tended to decrease again close to and at the source area. Nature and composition of the basement bedrock with foliation planes dipping in the direction of slope, dominant joint sets oriented perpendicularly to the foliation, the nature of weathered material and high relief were strong factors in the avalanche. Field studies identified 43 landslides at the Iva Valley area of Enugu state, which were shallow, short run-out movements with slip-surface depth less than 2 m. The shallow slides and the avalanche are triggered by water infiltration in slopes with high topographic gradient. The soil saturation leads to a reduction of the shear strength of the soil because of a rise in pore water pressure. These landslides are known to occur during or after intense rainfalls at the beginning or at the tail end of rainy season.
Arabian Journal of Geosciences, 2014
The Iva Valley area has one of the highest densities of landslides in Nigeria, and impacts the re... more The Iva Valley area has one of the highest densities of landslides in Nigeria, and impacts the residents, local economy, and the environment. Slopes in the area sit on unconsolidated, cross-bedded, friable sandstone units with interbeds of claystone. Past research efforts had proposed theories explaining the mechanism of failure based on the limited-liquefaction behavior of the slope materials. But as landslide prevention works on the slopes began to fail, it became apparent that those theories were inadequate solutions to the devastating effect of mass wasting processes. This paper presents the results of landslide susceptibility assessment based on the new evidence of complete-liquefaction behavior observed in the samples when back-pressure is employed to accomplish full saturation. Loose, saturated specimens failed after attaining maximum strength at shear displacements less than 1 mm. The failure was marked by rapid reduction in shear strength and accompanied by a steady increase in pore water pressure until the ratio of pore pressure and normal stress approached unity indicating complete liquefaction. This behavior simulated the response of the slope soils to varying stress and drainage conditions in the field, and seems an adequate mechanism for the incessant failure of slopes and prevention works. Because the geology of a vast area of the SouthEast Nigeria is similar, the results obtained at the study area are also applicable in other areas within the region for sustainable preventive and mitigating measures.
Geosciences Journal, 2013
ABSTRACT The dominant factors initiating the transformation of landslides into catastrophic debri... more ABSTRACT The dominant factors initiating the transformation of landslides into catastrophic debris flow are examined. The research found that a threshold pore pressure determined from theoretical and experimental analysis was enough to initiate liquefaction type of failure in sandy materials. Loading tests to failure on sourcearea sandy soils from a catastrophic landslide location show that under definite conditions of loading, a threshold state, characterized by the equality and constancy of pore pressure and shear resistance develops in the sands at a threshold density. Sands at this density clearly define the boundary between contractive and dilative specimens under same effective normal stress. Confirmatory experiments were then conducted using silica sand. Analyses showed that samples in which the threshold pore pressure was exceeded readily liquefied while those in which the pore pressure was below the limit dilated. The concept of threshold pore pressure fills the gap created by classical theories of soils liquefaction that have identified densities at which phase transformation and steady state lines can be defined. The new concept shows there is a density at which both lines merge and it is proposed that sands transiting from dense to loose and vice versa will first pass through the threshold state. While the stability of a slope founded on sandy soils may be breached when the pore pressure exceeds a certain limit, it is possible to make estimates of the limit. Where such estimates are accompanied with adequate field measurements, the effectiveness of landslide prevention projects may be enhanced.
Environmental Science and Pollution Research
Modeling Earth Systems and Environment
Arabian Journal of Geosciences
Indian Geotechnical Journal
Geosystems and Geoenvironment
Advancing Culture of Living with Landslides, 2017
Complex rock-debris avalanches, debris flow, soils slip and earth slumps in Nigeria lead to the d... more Complex rock-debris avalanches, debris flow, soils slip and earth slumps in Nigeria lead to the destruction of lives and resources worth several millions of dollars annually. While long travel landslides, which are almost always catastrophic, mostly occur on igneous and metamorphic terrains at the boundary of Nigeria and Cameroon, the south east sedimentary terrains are subject to deep and wide gullies resulting from aggressive erosion and slumping movements. Slope failures in the two regions are therefore distinctively different with research revealing that the differences are in geology, structural geometry, style of deformation, slope gradient and the volumes involved. At the Nigeria-Cameroon border, complex, rock-debris avalanches are found on steep dipping slopes, where slope parallel, basal sliding planes along foliation and lineation surfaces control failure and mobility of materials downslope.
Bulletin of Engineering Geology and the Environment, 2022
Soil erosion is a life-threatening hazard ravaging and displacing many communities in Anambra Sta... more Soil erosion is a life-threatening hazard ravaging and displacing many communities in Anambra State, Nigeria. Most erosion studies in this region have been based on geological and geotechnical analyses of soils from gullies. In this paper, the soil erosion risk of Anambra State was evaluated using the Revised Universal Soil Loss Equation (RUSLE) and geoinformatics, to estimate the rate of soil loss and identify vulnerable erosion zones. The RUSLE model was based on five erosion factors (rainfall erosivity (R), soil erodibility (K), topography (LS), vegetation cover (C), and anti-erosion practices (P)). The R-factor ranged from 460.51 to 582.08 MJ/mm/ha−1 h−1 year−1 whereas the K-factor ranged from 0.100 to 0.310 t/h/MJ−1/mm−1. Low–moderate LS-factor values dominated the northern and western portions of the State. However, moderate–high LS-factor scores dominated the eastern and southern portions. The C-factor varied from 0 (in areas covered by water bodies) to 1 (for barren lands). The P-factor ranged from 0.5–1. These five factors were integrated to generate soil loss rates across Anambra. The average annual soil loss ranged from 0 to over 6 t/ha−1 year−1. The soil loss results showed that about 5% (242.2 km2), 25% (1211 km2), 30% (1453.2 km2), and 40% (1937.6 km2) of the total area have very low, low, medium, and high erosion risks, respectively. The northern and western portions of the State were characterized by very low, low, and moderate soil loss. However, the eastern and southern portions were characterized by high soil loss rate. It was indicated that LS, K, and R are the most important soil loss factors in Anambra.
Environmental Earth Sciences, 2021
Over many decades, land degradation, due to gully erosion and landsliding, has remained a serious... more Over many decades, land degradation, due to gully erosion and landsliding, has remained a serious threat to land-use management and economic sustainability in southeastern Nigeria. Several causative factors have been listed to be responsible for the continuous land degradation. In this study, multiple geostatistical and new indexical models were integrated to assess the role of soil engineering properties in the erosion of ten major gullies in southern Anambra State, southeast Nigeria. Gully soil samples were analyzed for properties such as particle size distribution, water content, Atterberg limits, compactness, bulk density, specific gravity, shear strength, porosity and permeability coefficients. The geotechnical analyses revealed that the gully materials are weak and have poor erosion-resistant features. The results revealed that the soils’ engineering properties influence their erodibility. Interparameter relationships observed from correlation, factor, and cluster analyses showed that the engineering parameters jointly impact the erosion processes. Novel indexical methods, sand-gravel ratio (SGR) and sand–fines ratio (SFR), alongside erodibility factor confirmed that the soils are erodible. A novel entropized soil loss rate (AE) model estimated high cumulative annual soil loss rate for the area at 0.9705. Overall, it was revealed that SW, SC, and SP soils are far more susceptible to gully erosion than CL and GP soils in the area. Artificial neural network models were developed and used to accurately (with low model errors and R2 range of 0.956–0.997) predict the SGR, SFR and AE. The findings of this research would be helpful in advancing soil erosion investigations and in planning for effective mitigation measures, with respect to engineering properties.
Environmental Forensics, 2021
The effect of waste dumps on groundwater quality on perched aquifers in Nsukka and environs was i... more The effect of waste dumps on groundwater quality on perched aquifers in Nsukka and environs was investigated by applying multivariate statistical analyses using Statgraphics Centurion XVII, ArcGIS ...
Goldschmidt Abstracts, 2020
Gully erosion is a major environmental problem in Gombe town, large area of land is becoming unsu... more Gully erosion is a major environmental problem in Gombe town, large area of land is becoming unsuitable for human settlement, hence the need for gully erosion susceptibility map of the study area.To generate gully inventory map, detailed field exercise was carried out, during this investigation one hundred gullies were identified and studied extensively within the study area of about 550 km2. In addition to the mapped gullies, Google EarthPro with high resolution imagery was used to locate the spatial extents of fifty (50) more gullies. Ten gully erosion predisposing factors were carefully selected considering the information obtained from literature, and multiple field survey of the study area, the factors include: elevation, slope angle, curvature, aspect, topographic wetness index (TWI),soil texture, geology, drainage buffer, road buffer and landuse.In this study, a GIS-based Frequency Ratio (FR) and Analytical Hierarchy process (AHP) models were employed to predict areas prone t...
Modeling Earth Systems and Environment, 2020
Quality of the soil and its effect on groundwater pollution were evaluated using combined techniq... more Quality of the soil and its effect on groundwater pollution were evaluated using combined techniques of geotechnical, physicochemical, pollution indices and statistical models. Geotechnical result showed that particle sizes of soil in the study area are well graded. The physicochemical parameters (Zn, Cu, Cd, Pb, Mn, Fe, Cr and Ni) are higher in the control than in study area except for the soil pH. These parameters are within the standard set by Department of Petroleum Resources in Nigeria (DPR) for metal concentration in the soil. The ecological risk factor reviewed that toxicity of the element is potentially very low and PIavg and PIVector of the soil samples showed they are not contaminated. In contrast, the concentrations of these parameters including total dissolved solid TDS, biochemical oxygen demand BOD, turbidity were higher in groundwater samples from the study area than in control except for the groundwater pH (55.929) which was lower than in control (5.956). One of the 15 samples is out of the standard for Ni, Cu, Cd, Pb and Mn and two (2) for turbidity, Cr and Fe. Principal component analysis shows five factors accounting for 94.923% of the total variance. At 0.05 levels, very strong significant correlation and at 0.01 levels moderate to weak correlation exist between the elements. The result showed that groundwater from well-graded soil is of good quality irrespective of the industrial activities, whereas those from poorly graded soil are of poor quality.
Modeling Earth Systems and Environment, 2020
In Udi province, gully erosion has caused several environmental damages such as loss of agricultu... more In Udi province, gully erosion has caused several environmental damages such as loss of agricultural lands and natural vegetation, loss of residential apartments, destruction of engineering structures, and disruption of wildlife ecosystem. In this paper, an attempt was made to assess the erodibility characteristics and slope stability of geological units prone to erosion in this area using integrated approach. Geotechnical analysis of soil samples revealed that they are susceptible to erosional processes. The soil samples were classified as poorly graded sands and silty sands based on Unified Soil Classification System. Grain size distribution analysis showed that the soils were almost devoid of clays, which could serve as binding materials. Atterberg limit test revealed that they were nonplastic. Compaction test indicated that the soils were loose and collapsible, with dry density ranging from 1.65 to 1.96 g/cm 3. On the basis of permeability coefficients (which ranged from 6.81 × 10-5 to 1.28 × 10-4 m/s), the soils are moderately to highly permeable, indicating high infiltration capacity. Shear strength analysis revealed that the soils have low cohesive capacity (ranging from 0 to 5 kPa) and relatively low angle of shearing resistance (ranging from 22° to 30°). Multivariate statistical analyses aided the establishment of the interrelationships between the analyzed geotechnical parameters. The obtained factor of safety of the gully slopes (in both saturated and unsaturated conditions) ranged from 0.81 to 0.90 and 1.02 to 1.41, respectively. This indicates that the gully slopes are typically unstable in saturated conditions and critically stable in unsaturated conditions.